A variety of fluid flow control valves and corresponding valve actuators are utilized for on/off control or throttling the flow of fluid, such as in a gas or oil pipeline system, or in other process fluid systems. The fluid flow control valves are typically sliding stem control valves or rotary action control valves and are operated by a valve actuator such as a pneumatic piston or diaphragm actuator responding to the output of a valve positioner or valve controller instrument for accurate throttling control of the valve.
In the case of rotary action control valves, these units typically employ a flow control member in the form of a rotatable ball, rotatable ball segment, or a rotatable butterfly element. The rotation of the flow control element opens and closes the valve gate or plug.
Valve actuators for controlling such rotary action control valves typically employ a movable diaphragm connected to a rod at the diaphragm center. Moving the diaphragm displaces the rod linearly and thus requires a linear to rotary action translation. A rotational link arm has one end fixed to the valve rotary shaft and the other link arm end is coupled to the diaphragm rod. Linear movement of the diaphragm rod moves the link arm and thereby actuates a rotational movement in the valve shaft which is ultimately connected to the rotatable flow control element in the fluid control valve.
Such presently available rotary valve actuators employ many components, several of which require time consuming and expensive machining during manufacture. A manufacturer and users of rotary valve actuators therefore must inventory a large number of parts, and also must inventory an increasing number of expensive, machined spare parts for repair and replacement.
It is desired therefore to reduce the number of parts as well as to reduce the number of time consuming and expensive machined parts in a rotary valve actuator so as to thereby reduce manufacturing costs and inventory requirements both for the manufacturer and the user. In addition, it is further desired to provide a rotary valve actuator of reduced size and weight, and one having the capability of actuating a variety of rotary valves to reduce the number of rotary valve actuators required.